The essence of that article and the linked paper is that you can't make a large rocky body by assembling many small icy ones.

Here's a go at that problem. Start with a population of small particles, mostly silicate (rockdust), some ice. Suppose that rock-rock collisions are very bad at resulting in coalescence whereas ice-ice and ice-rock collisions do so more easily due to the absorption of energy by plastic deformation and partial melting. The rock particles would never find a permanent home until they ran into an already formed icy object. As the object grows it becomes better and better at trapping the ubiquitous rockdust.

Suppose that rock-rock collisions are very bad at resulting in coalescence whereas ice-ice and ice-rock collisions do so more easily due to the absorption of energy by plastic deformation and partial melting.

Is there anything in the literature to suggest those suppositions are true.

2/ OK here's my winter project, following up on Mike Brown's entertaining terrestrial snowball anecdotes. I will try to make two snowballs collide and coalesce in mid-air. I expect it will require many attempts and I will need some help from the family.

If anyone would like to volunteer for the control group your task is to make it happen with two stones.

Is there anything in the literature to suggest those suppositions are true.

I'm sure ngunn's suggestion is on Mike Brown's list of possibilities, but no, there probably isn't any solid info to support it at the moment. As I understand it, we know how to form "pebbles" up to around 1 cm (from lab experiments and some theory), and then how to form larger bodies once you've gotten up to 1 km planetesimals (from bulk material properties), but in between is full of question marks. I can't remember the proper buzzwords for a good ADS search but one recent example paper is "Growth and fragmentation of centimetre-sized dust aggregates: the dependence on aggregate size and porosity," Farzana Meru, et al., MNRAS 435, 2371 (2013).

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